| 摘要 |
<p>A lower section (14) of the tower hinges on the superstructure and has struts attached to its top end on posite sides. A transverse shaft at the free end of these struts accommodates one row of pulleys in a first pulley block mechanism, the shaft of the other row being fixed to the superstructure. The upper section (16) of the mast hinges on and is lockable to the lower one and has a further strut attached at a point above the hinge (20) and coupled to a fixed boom on the superstructure. An erection beam (28) is attached to the superstructure on either side and at the top end these accommodate between them a shaft with pulleys forming part of a second pulley block. One end of the rope (40) reeved round these pulleys and others on the superstructure is fixed to a winch drum on the latter and the other to a cross-member pulled by the rope closer to the pulleys at the top end of the beams.</p> |
